1. Field of the Invention
The present invention relates to a comparator circuit of a various types, a static type, a dynamic type, a amplifier type and so on, which is capable of performing a test operation without using a reference signal which is usually compared with an input signal transmitted to the comparator circuit.
2. Description of the Prior Art
There is a conventional comparator circuit of a static type which is constructed by using Field Effect Transistors (FETs), as shown in FIG. 19.
In FIG. 19, the conventional comparator circuit has a configuration comprising a p-channel FET 102 for receiving an input signal which is transmitted from outside through an input terminal 101, a p-channel FET 104 for receiving a reference signal provided to a reference terminal 103, whose level is set as a fixed level between a high level and a low level of the input signal and which is compared to the level of the input signal, a p-channel FET 105 connected between a high voltage power source V.sub.DD and source terminals of the p-channel FETs 102 and 104 whose source terminals are commonly connected to each other, a n-channel FET 106 which is located between a drain terminal of the p-channel FET 102 and a ground GND, a n-channel FET 107 which is located between a drain terminal of the p-channel FET 104 and a ground GND and a gate terminal of the n-channel FET 107 is connected to the drain terminal of the p-channel FET 104 and the gate terminal of the n-channel FET 106, and an inverter circuit 109 which is connected between an output terminal 108 and the drain terminals of the p-channel FET 102 and the n-channel FET 106 which are commonly connected.
In the conventional comparator circuit having the configuration described above, there is a condition that the conventional comparator circuit receives the input signal the high level of which is 1.2 Volt and the low level is 0.4 volt, and the voltage level of the reference signal is 0.8 volt which is an intermediate voltage between the high level and the low level of the input signal, for example.
Under the condition described above, when the input signal of the high level is transmitted to the input terminal 101, the p-channel FET 102 approaches a non-continuity state or an OFF state, but not enters the non-continuity state where the voltage level between the drain and source of the p-channel FET 102, the n-channel FETs 106 and 107 enter a continuity state or an ON state where a current flows, and the level of the output signal provided to the output terminal 108 becomes the high level.
On the other hand, when the conventional comparator circuit receives the input signal of the low level through the input terminal 101, the p-channel FET 102 enters the continuity state and the n-channel transistors 106 and 107 enter the non-continuity state, and the level of the output signal provided to the output terminal 108 becomes the low level.
When a burn-in-test, which is one of tough and durable tests for testing durability of comparator circuits, to this conventional comparator is performed, the conventional comparator circuit is connected to a burn-in-test board where a burn-in-test device is incorporated, and then the burn-in-test device generates test signals and transmits the test signals to the conventional comparator circuit through the burn-in test board.
In the burn-in-test of such a manner, the burn-in test device has a limit that it can generate only two levels of the input signal to be provided to the comparator circuit, the high level and the low level which are different to each other. For this reason, when the comparator circuit as the conventional type one described above is tested, because the conventional comparator circuit requires three different levels, the high level and the low level of the input signal and the reference level of the reference signal, the burn-in-test board side must generate the reference signal of the reference level other than the high and low levels of the input signal.
FIG. 20 is a configuration diagram of a conventional comparator circuit of a dynamic type. In this case, like the case of the conventional comparator circuit of a static type as shown in FIG. 19, when the burn-in test operation is executed, signals of three levels such as a high level, a low level and a reference signal level must be generated by a burn-in test board side. Moreover, the burn-in test board transmits these signals of the three levels to the comparator circuit during the test operation.
In addition, FIG. 21 is a configuration diagram of a conventional comparator circuit of an amplifier type. In this case, like the case of the conventional comparator circuit of a static type as shown in FIG. 19, when the burn-in test operation is executed, signals of three levels such as a high level, a low level and a reference signal level must also be generated by a burn-in test board side. Then, the burn-in test board transmits the signals of these three levels to the comparator circuit during the test operation.
In general, because many commercially available burn-in-test boards have no function for generating any signal having the reference level other than the high level and the low level of the input signal, these available burn-in test boards can not be used for the burn-in test of the conventional comparator circuit. Therefore an exclusive burn-in test board must be used for the burn-in-test of the conventional comparator circuit.
As described above in detail, in the conventional comparator circuit using three different levels of the signals, when the many commercially available burn-in-test boards is used for the burn-in test, it must be required to use the exclusive burn-in test board which is capable of generating the signals to be required for and used in the comparator circuit during the test operation mode. For this reason, it takes a lot of time and costs more to make the exclusive burn-in test board. This is a problem.